The design of picture reproduction systems Involves consideration of a number of factors which affect how a picture is perceived by the human eye, including but not limited to the following factors: (1) sharpness or pictorial clarity, (2) contrast between light areas, dark areas and the related background illumination, and (3) realistic color values. In this context it should be noted that the eye does not respond equally to radiated energy of all visible wavelengths, there is a wide variation in response between observers, and the eye's response is a function of light intensity. See W. C. Hughes, "Electronic Engineers' Handbook", 1st Ed., pp. 20-3, 20-4, McGraw-Hill 1975.
Color video (television) standards are based on the manner in which the eye perceives colored light. In color video systems a wide range of colors can be reproduced for reception by the eye by the addition of only three monochromatic light sources, red, green and blue. The color signals produced by a video camera are encoded before being transmitted to a television receiver or other video display device, the encoded signals comprising a luminance information signal and color signals. As explained by Hughes (supra), p.20-3, the luminance of a surface is the effect on the average eye of the light emitted by a unit area of the surface. Luminance is the integrated effect of the eye response and the visible light power radiated by the surface, both of which are functions of wavelength.
Spatial frequency is the frequency at which an image changes over distance. Luminance is more significant than color at higher spatial frequencies. The human eye response to high spatial frequency information is not the same as it is for low spatial frequency information. Accordingly efforts have been made to process spatial frequency video information signals for the purpose of enhancing the sharpness of reproduced video images. One such effort is represented by U.S. Pat. No. 4,721,998, issued Jan. 26, 1988 to W. E. Glenn for "Method And Apparatus For Processing Color Video Signals". Other such efforts may be known to persons skilled in the art.
The idea of enhancing the images produced by a video camera is particularly intriguing in the case of producing images for surgical or medical purposes. For such purposes, video cameras are utilized in the form of video endoscopes, so-called because the camera is embodied as an integral part of the endoscope, or as an accessory that is attached to the back end of a conventional optical endoscope. In many surgical procedures it is often helpful to enhance color video images in a way which will add to the information perceived by the medical specialist. Details such as small or large blood vessels, differences in tissue condition or tissue types, and the margins between them can be made more distinct and informative by appropriately electronically enhancing the image reproduced by use of the video signals.